Beclin-1 expression is retained in high-grade serous ovarian cancer yet is not essential for autophagy induction in vitro

• Published in: Journal of ovarian research Vol. 8; no. 1; p. 52
• Main Authors: Correa, Rohann J M, Valdes, Yudith Ramos, Shepherd, Trevor G, DiMattia, Gabriel E
• Format: Journal Article
• Language: English
• Published: England BioMed Central Ltd 04.08.2015; BioMed Central
• Subjects: Apoptosis - genetics; Apoptosis Regulatory Proteins - biosynthesis; Apoptosis Regulatory Proteins - genetics; Autophagy - genetics; Beclin-1; Cancer; Cell Line, Tumor; Cell Survival - genetics; Cystadenocarcinoma, Serous - genetics; Cystadenocarcinoma, Serous - pathology; Development and progression; Female; Fluorescence microscopy; Gene expression; Gene Expression Regulation, Neoplastic; Genes; Genetic aspects; Genomes; Genomics; Health aspects; Humans; Membrane Proteins - biosynthesis; Membrane Proteins - genetics; Ovarian cancer; Ovarian Neoplasms - genetics; Ovarian Neoplasms - pathology; Spheroids, Cellular - pathology
• ISSN: 1757-2215; 1757-2215
• DOI: 10.1186/s13048-015-0182-y

Autophagy is a conserved cellular self-digestion mechanism that can either suppress or promote cancer in a context-dependent manner. In ovarian cancer, prevalent mono-allelic deletion of BECN1 (a canonical autophagy-inducer) suggests that autophagy is impaired to promote carcinogenesis and that Beclin-1 is a haploinsufficient tumor suppressor. Nonetheless, autophagy is known to be readily inducible in ovarian cancer cells. We sought to clarify whether Beclin-1 expression is in fact disrupted in ovarian cancer and whether this impacts autophagy regulation. BECN1 expression levels were assessed using The Cancer Genome Atlas (TCGA) datasets from 398 ovarian high-grade serous cystadenocarcinomas (HGSC) and protein immunoblot data from HGSC samples obtained at our institution. Knockdown of BECN1 and other autophagy-related gene expression was achieved using siRNA in established human ovarian cancer cell lines (CaOV3, OVCAR8, SKOV3, and HeyA8) and a novel early-passage, ascites-derived cell line (iOvCa147-E2). LC3 immunoblot, autophagic flux assays, transmission electron microscopy and fluorescence microscopy were used to assess autophagy. We observed prevalent mono-allelic BECN1 gene deletion (76%) in TCGA tumors, yet demonstrate for the first time that Beclin-1 protein expression remains relatively unaltered in these and additional samples generated at our institution. Surprisingly, efficient siRNA-mediated Beclin-1 knockdown did not attenuate autophagy induction, whereas knockdown of other autophagy-related genes blocked the process. Beclin-1 knockdown instead decreased cell viability without inducing apoptosis. Taken together, these data demonstrate that despite its sustained expression, Beclin-1 is dispensable for autophagy induction in ovarian tumor cells in vitro, yet may be retained to promote cell viability by a mechanism independent of autophagy or apoptosis regulation. Overall, this work makes novel observations about tumor expression of Beclin-1 and challenges the accepted understanding of its role in regulating autophagy in ovarian cancer.